Researchers have come up with hard evidence that what women really want from a mate is somebody who reminds them of their father.

They have discovered that women sniff out men whose body odour is similar to that of their fathers.

The theory is that a man who smells similar to a woman's father is likely to have a compatible immune system.

The nature odours that all humans produce are called pheromones. They are influenced to a degree by a cluster of genes related to the immune system called the Major Histocompatibility Complex (MHC).

Diversity

Previous research found that women prefer the smell of men who have different immune system genes from their own.

This was thought to ensure that their offspring have as wide a range of immune response genes - and therefore greater protection against infection - as possible.

However, the new results show that the odour selection of women is even more finely tuned than was previously thought.

A total of 49 unmarried women were tested by asking them to smell T-shirts worn by men for two consecutive nights.

The US researchers, led by Dr Martha McClintock from the University of Chicago, found that women preferred men with a genetic smell somewhat the same - but not identical - to their own.

Dr McClintock said: "We had men wear the t-shirts at night while they were sleeping.

"So the scents that we collected were really quite mild. They would be like what you would smell on someone's pillow or sheet."

Analysis showed a significant correlation with odour components produced by immune system genes inherited from the women's fathers.

The scientists suggest that being attracted to some of father's gene smells may be a safe gamble for a woman to ensure her offspring gets a tried and tested immune system.

Strong immunity

On the other hand, she would also want enough different genes to give her baby a wide range of immune responses.

Being attracted to men who smell slightly, but not too much, like her father represented a good compromise.

Dr McClintock said the whole process seemed to work on an unconscious level.

"These scents were not detectable as human scents. The women knew they were scents, but had no idea that they were human scents."

It seems that humans are no different to other animals. Research in mice has shown that females prefer males that are just slightly unfamiliar over those that are either very familiar or very unfamiliar.